1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for manufacturing a grounding device, and more particularly, to an LCD device that has a plurality of grounding protrusions in a region of the bottom surface of a printed circuit board that contacts a bottom chassis and does not have a signal transmission pattern. This increases a contact area between the printed circuit board and the bottom chassis and minimizes a damage caused by an electromagnetic wave.
2. Description of the Related Art
Generally, an LCD device is well accepted as a flat panel display. Especially, the smaller size, lighter weight and lower power consumption render the LCD device to replace the traditional cathode ray tube (CRT). LCD devices have been sufficiently developed to serve as a flat panel display device, and are used as a monitor for a lap-top computer and even for a desktop computer. Thus, LCD devices are gaining popularity.
Unlike CRTs, LCD devices are light emitting elements that adjust the amount of the light applied from an external device and display images on the screen. Therefore, an additional light source, say, a backlight unit, for irradiating the light onto the LCD panel is required.
Such a backlight assembly is composed of a mold frame, a lamp assembly contained in the mold frame and emitting a light, a light guide contained in the mold frame and guiding the light toward an LCD panel, a bottom chassis installed at the bottom surface of the mold frame and supporting members contained in the mold frame, and a top chassis combined with the mold frame to support the LCD panel.
An LCD device employed as a monitor for a desktop computer has a mold frame and a metal bottom chassis. A metal structure builds a stronger LCD device and shields the device from an electromagnetic wave. It further helps an LCD device discharge a large amount of heat generated when a lamp assembly emits a strong light to match a CRT display.
As shown in FIG. 1, if a printed circuit board (PCB) 90 connected to the LCD panel through a tape carrier package (TCP) 75 to drive an LCD panel (not shown) is positioned at the rear surface of a bottom chassis 60, via holes 92 formed at the bottom surface of PCB 90 as shown in FIG. 2 contact bottom chassis 60, which may short electric signals. Therefore, an insulator sheet 85 is inserted between bottom chassis 60 and PCB 90. Reference numeral 80 denotes a top chassis.
Most of driving elements 94 mounted onto PCB 90 to drive the LCD panel operate at a high frequency, and thus generate an electromagnetic interference (EMI). Such an EMI may interfere the electric signal transmitting to the LCD panel, and further cause an error in other devices when discharged to the outside of an LCD device 1.
To reduce EMI, as shown in FIG. 2, a metal film 97 at the corner of PCB 90 is exposed by partially removing a solder resist film on metal film 97, and a screw hole 96 is formed at the exposed portion of metal film 97. Then, PCB 90 is fixed to bottom chassis 60 using a screw 95, in order to ground an EMI to bottom chassis 60.
A grounding via hole 92′ connects a grounding pattern (not shown) formed at the top surface of PCB 90 and metal film 97 formed at the bottom surface of PCB 90, and has a bridge 93 that connects metal film 97 at its periphery.
However, as described above, since the PCB contacts the bottom chassis only at its corners, the contact area between the PCB and the bottom chassis is limited. Thus, a large amount of EMI generated from the PCB are not grounded to the bottom chassis and may cause an interference with an electric signal applied to the LCD panel. As a result, an LCD device has a degraded screen quality, and the EMI discharged to the outside of the LCD device may cause an error in other devices.
The PCB contacts the bottom chassis only at its corners because a light guide is installed all over the whole area of a mold frame except its edges corresponding to edges of the PCB.
Moreover, an LCD device used for a monitor has a problem of low productivity caused by an insulator sheet mounting process between the bottom chassis and the PCB in order to insulate the bottom chassis from the PCB.